GAW Report No. 227
WMO/GAW Aerosol Measurement Procedures, Guidelines and Recommendations
It is the goal of the Global Atmosphere Watch (GAW) programme to ensure long - term measurements in order to detect trends in global distributions of chemical constituents in air and the reasons for them (WMO, 2001a). With respect to aerosols, the objective of GAW is to determine the spatio - temporal distribution of aerosol properties related to climate forcing and air quality on multi - decadal time scales and on regional, hemispheric and global spatial scales. The objective of GAW Report No. 153, published in 2003, was to provide a synthesis of methodologies and procedures for measuring the recommended aerosol variables within the GAW network. The report has been extensively used by the scientific community, and more particularly by scientists and engineers involved with data production from ground - based sites. The knowledge of aerosol impact on climate and air quality as well as the techniques used for the determination of the essential aerosol variables to be monitored at ground - based sites have considerably evolved in the last decade, justifying an update of GAW Report No. 153. This update has been prepared shortly after the release of the Working Group 1 report from the International Panel on Climate Change (IPCC, 2013). A clear emphasis was given for the first time in IPCC reports since 1992 to the analyses of evidence of climate change from observations of the atmosphere highlighting the challenges for d eveloping long - term, high quality observation record that can be used to constrain models at global and regional scales. While the benefit of improved monitoring capabilities developed in the last decades, both from satellites and ground - based has been cl early assessed for the production of more reliable data records, the report still highlights the need for maintaining and enhancing the capacity of the observing system to provide the additional constrains, in particular for the derivation of trends.